Abstract

The poles of the mitotic spindle contain one old and one young centrosome. In asymmetric stem cell divisions, the age of centrosomes affects their behaviour and their probability to remain in the stem cell. In contrast, in symmetric divisions, old and young centrosomes are thought to behave equally. This hypothesis is, however, untested. In this study, we show in symmetrically dividing human cells that kinetochore-microtubules associated to old centrosomes are more stable than those associated to young centrosomes, and that this difference favours the accumulation of premature end-on attachments that delay the alignment of polar chromosomes at old centrosomes. This differential microtubule stability depends on cenexin, a protein enriched on old centrosomes. It persists throughout mitosis, biasing chromosome segregation in anaphase by causing daughter cells with old centrosomes to retain non-disjoint chromosomes 85% of the time. We conclude that centrosome age imposes via cenexin a functional asymmetry on all mitotic spindles.

To calculate in hTert-RPE1-eGFP-centrin1 cells the relative differences in microtubule nucleation, cells were stained after a release from an ice-cold treatment with a-tubulin antibodies (microtubules) and DAPI (chromosomes). The intensity of the centrosomal aster (minus the background) at old and young centrosomes was measured and the relative differences calculated with the indicated formula. Scale bar = 5 μm.DOI: http://dx.doi.org/10.7554/eLife.07909.009

(A) hTert-RPE1-eGFP-centrin1 cells treated with 10 ng/ml nocodazole and stained for CENP-E and DAPI. White arrowheads indicate old centrosomes in all panels. Scale bars in all panels = 5 μm. (B) Differences in the abundance of CENP-E and CREST (kinetochore marker) at kinetochores bound to old and young centrosomes, calculated from 27 cells in 3 independent experiments. Columns indicate the median; error bars the 99% CI. (C) Immunofluorescence image of a HeLa-eGFP-centrin1/eGFP-CENP-A (green) cells treated with 10 ng/ml nocodazole, fixed with glutaraldehyde, and stained for α-tubulin (red) and DAPI (blue). Single kinetochores in every unaligned sister-kinetochore pair were classified as end-on attached, laterally attached or unattached. Inset 1 on the left shows an illustrative example of a kinetochore pair with one unattached and one end-on attached kinetochore; inset 2 on the right shows an illustrative example with 2 laterally attached kinetochores. (D) Quantification of individual end-on attached kinetochores at old and young centrosomes in HeLa-eGFP-centrin1/eGFP-CENP-A cells treated with 10 ng/ml nocodazole, 5 nM taxol and the indicated siRNAs and 10 ng/ml nocodazole. Percentages are based on 3 independent experiments with 29–50 cells. Error bars indicate s.e.m; *** indicates p ≤ 0.01 in paired t-test. (E) hTertRPE1-eGFP-centrin1 cells stained with anti-acetylated tubulin (red) and CREST (green) antibodies. Shown are total projections (upper panels) or maximum-intensity projections of 5–10 planes around the focal plane of interest (lower panels). White arrowheads indicate kinetochore–microtubules with stronger acetylation, yellow with weaker acetylation. Note that the white arrows are on the side of the old centrosome. (F) Differences in the abundance of acetylated tubulin on k-fibres of sister-kinetochores, and detyrosinated tubulin on the two spindle halves in hTertRPE1-eGFP-centrin1 cells, based on 3 independent experiments and 32–33 cells. Methodology is explained in . Columns indicate the meadian, error bars the 99% CI. (G) HeLa-eGFP-centrin1/eGFP-CENP-A cells treated with 0.5 mM Ca2+ for 10 min stained for α-tubulin (red) and DAPI (blue). Shown are total projections (upper panels) or maximum-intensity projections of 5–10 planes around the focal plane of interest (lower panels). White arrowheads in zoom-ins indicate end-on attached kinetochores and yellow arrow the unattached kinetochore. (H) Percentage of unattached kinetochores oriented towards old or young poles based on 3 independent experiments and 33 cells. (I) hTert-RPE1-eGFP-centrin1 cells stained with CENP-A antibodies (red) and DAPI (blue) after treatment with 5 nM taxol or the indicated siRNAs and 10 ng/ml nocodazole. White arrowheads indicate old centrosome. (J) Proportion of unaligned chromosomes at old centrosome in hTert-RPE1-eGFP-centrin1 cells treated with 5 nM taxol or with 10 ng/ml nocodazole after the indicated siRNA treatment. Error bars indicate s.e.m; *** indicates p ≤ 0.01 in Binomial test. (K) Differences in the abundance of cenexin, phospho-Aurora-A, and Plk1 at old and young centrosomes in HeLa and hTert-RPE1-eGFP-centrin1 cells, based on 3 independent experiments and 41–113 cells. Methodology is explained in . Columns indicate the median, error bars the 99% CI. (L) Proportion of unaligned chromosomes at old centrosome in HeLa-eGFP-centrin1 cells treated with Aurora-A or Plk1 inhibitors. Error bars indicate s.e.m; *** indicates p ≤ 0.01 in Binomial test. For results of all individual experiments see .DOI: http://dx.doi.org/10.7554/eLife.07909.01010.7554/eLife.07909.011Figure 3—source data 1.Values of individual experiments of graphs shown in .DOI: http://dx.doi.org/10.7554/eLife.07909.011

Methodology to compare kinetochore- and centrosome-associated protein intensities at old and young spindle poles.

(A) To calculate in hTert-RPE1-eGFP-centrin1 cells the relative differences in the abundance of CENP-E on unaligned kinetochores, cells were stained with CENP-E antibodies and DAPI (chromosomes). The intensity of CENP-E on unaligned kinetochores (minus the background) at old and young centrosomes was measured and the relative differences calculated with the indicated formula. Scale bars in all panels = 5 μm. (B) Methodology to calculate the relative differences in phospho-Aurora-A, Plk1, or cenexin in hTert-RPE1-eGFP-centrin1 cells as displayed in . In this example, cells were stained with phospho-Aurora-A antibodies, before determining its abundance on old and young centrosomes. The relative difference was calculated with the indicated formula. (C) Methodology to calculate the relative differences in acetylated tubulin (ac-tubulin) in hTert-RPE1-eGFP-centrin1 cells as displayed in . In this example cells were stained with acetylated tubulin antibodies, before determining its abundance on the kinetochore–microtubules associated with old and young centrosomes. The relative difference was calculated with the indicated formula. (D) Methodology to calculate the relative differences in detyrosinated tubulin (dt-tubulin) in hTert-RPE1-eGFP-centrin1 cells as displayed in . Cells were stained with detyrosinated tubulin antibodies, before determining its abundance on the half-spindles associated with old and young centrosomes. Same area around the old and the young centrosome, containing centrioles, was excluded from the measurement (green rectangles). The relative difference was calculated with the indicated formula.DOI: http://dx.doi.org/10.7554/eLife.07909.012

Quantification of the proportion of laterally and unattached kinetochores.

Proportion of laterally attached (left) or unattached kinetochores (right) at old and young centrosomes in HeLa-eGFP-centrin1/eGFP-CENP-A cells treated with 10 ng/ml nocodazole, as determined in immunofluorescence pictures shown in .DOI: http://dx.doi.org/10.7554/eLife.07909.013

(A) Time lapse images of a HeLa-eGFP-centrin1/mCherry-CENP-A cell with a non-disjoined sister-kinetochore pair in anaphase. White arrowhead indicates the old centrosome, yellow arrowheads the non-disjoined sister-kinetochore pair. Scale bar = 10 μm. (B) Illustrative example of a HeLa-eGFP-centrin1/eGFP-CENP-A cell in anaphase stained for α-tubulin with a non-disjoined chromosome. Insets highlight the non-disjoined chromosomes. Scale bar = 5 μm. (C) Proportion of non-disjoined chromosomes that co-segregate with the old centrosomes in HeLa-eGFP-centrin1/mCherry-CENP-A cells treated with the indicated siRNAs. For statistics and number of experiments, see . (D) Proposed model of how old and new centrosomes differentially affect chromosome alignment and chromosome segregation via kinetochore–microtubule stability.DOI: http://dx.doi.org/10.7554/eLife.07909.016